Speed up backup process on BE-2010

Running on Server 2008R2 with 4GB NIC team (Link Agg) - I would think that most of the backups would have improved throughput, but not true. Have a 1.5+TB file server disk backup that consistently lags on throughput. On M-Th we use Inc-Diff-Inc-Diff straight to an MD1000 disk array attached to the backup server directly. The Friday is a full backup to the same disk array followed by D2Tape (TL4000) I have tinkered with job settings but some servers respond differently than others and I've found no real rhyme or reason why some are faster/slower than others. Here is our infrastructure environment and hopefully someone can point out my stupidity and the way to faster backups...... 8)
We have a dual active mirrored SAN (iSCSI) that is controlled by SANMelody (Running on PE2950's w/16GB RAM and Server 2008R2) Also have 6 ESX hosts (VI3 environment)- 4 ea. PE2950's (32GB RAM) and 2 ea. R710's (48GB RAM)
Have appox. 30 VM servers, one of which is our file server (Server 2003R2 32bit) and due to the recent change to VI3, we are still using agent based (Windows) backup on all servers. We also have a Notes VM server that I would consider fairly fast on backups (2,400MB/Min average) compared to the file server backups which the M-Th. daily's average around 350MB/Min

Wanted to add that we are considering using the NDMP option to speed up for certain servers unless this is not a viable option. I have seen that NDMP is mostly discussed with regards to NAS devices, but looking at the spec, I don't see that it is limited to NAS :?: